Source : Free On-Line Dictionary of Computing

periodic group
     
         (PE) Groups of logically related fields which occur
        multiple times within a group.
     
        Periodic groups are a non-{relational} technique.  An example
        of a PE would be for storing the history of a person's name
        changes, where name was kept in logically related fields such
        as surname, first name and middle name - with the person
        having changed their name more than once.
     
        [Clarification?]
     
        (1995-10-30)